Maleimide modified epoxy compounds were prepared by reacting N-(4-hydroxyphenyl) maleimide (HPM) with diglycidylether of bisphenol-A. Triphenylphosphine was used as catalyst and methylethylketone as solvent. The resulting compound possessed both the oxirane ring and maleimide group. The curing reaction of the maleimide epoxy compound with amine curing agents such as 1-(2-aminoethyl) piperazine (AEP) and 5-amino-1,3,3-trimethylcyclohexane methylamine isophorone diamine, IPDA) were studied. Incorporation of maleimide groups in the epoxy resin provides cyclic imide structure and high cross-linking density to the cured resins. The cured samples were found to have good thermal stability, chemical resistance (acid/alkali/solvent) and water absorption resistance

Gowda, N.

Kammasandra, S.

Mahendra, K.N.

ePrints@Bangalore University

1542     Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10 S. K. N. Gowda and K. N. MahendraPreparation and Curing Studies of Maleimide Bisphenol–A Based Epoxy ResinsShivananda Kammasandra Nanjunda Gowda and Kadidal Nagappa Mahendra*Department of Studies in Chemistry, Central College Campus, Bangalore University, Bangalore-560001, Karnataka, India*E-mail: mahendra_kadidal@yahoo.co.inReceived February 15, 2006Maleimide modified epoxy compounds were prepared by reacting N-(4-hydroxyphenyl) maleimide (HPM)with diglycidylether of bisphenol-A. Triphenylphosphine was used as catalyst and methylethylketone assolvent. The resulting compound possessed both the oxirane ring and maleimide group. The curing reaction ofthe maleimide epoxy compound with amine curing agents such as 1-(2-aminoethyl) piperazine (AEP) and 5-amino-1,3,3-trimethylcyclohexane methylamine isophorone diamine, IPDA) were studied. Incorporation ofmaleimide groups in the epoxy resin provides cyclic imide structure and high cross-linking density to the curedresins. The cured samples were found to have good thermal stability, chemical resistance (acid/alkali/solvent)and water absorption resistance.Key Words : Epoxy resin, MaleimideIntroductionEpoxy resins are widely used in industrial applicationsowing to their many attractive properties, such as excellentchemical and solvent resistance, good thermal and electricalproperties.1 At present epoxy resins are extensively used invarious technical applications such as coatings, compositesand as structural adhesives.2 The use of epoxy resin in highperformance structural materials has been increasingrecently. There is a lot of scope and need for improving theproperties of epoxy resins to be used in advancedapplications. For example, epoxy resin with superior thermalstability is needed for using as molding compounds andencapsulation materials in advanced electronic components.Generally, modifying epoxy resin with polyamides or imidocompounds2-3 provide a convenient approach of enhancingthe thermal stability of epoxy resins. Therefore, epoxy resinswere cured with reactive polyimides,2-4 polyamic acid,5 andimido-modified curing agents6 to introduce imide structureinto epoxy resin. The thermal stability of the above mentionedimido epoxy resins was significantly leveled up both in theintial decomposition temperature (IDT) and the integralprocedural decomposition temperature (IPDT).7 On the otherhand, epoxy resins modified with maleimide compounds havealso received attractive attentions, due to the similar curingconditions and processing properties of the epoxy resins andmaleimides.8-12 Maleimide epoxy resins generally showedappropriate properties between epoxy and maleimide resins.13Thus both the intercrossed and the interpenetrating systems(IPN) based on bismaleimides and epoxy resins wereprepared and they exhibited good thermal and mechanicalproperties.8-12In the present work, a maleimide compound with hydroxylgroup was first synthesized. Maleimide epoxy compoundswere consequently obtained through a simple additionreaction between the oxirane ring of epoxy compounds andhydroxyl group of maleimide. The resulting maleimide epoxycompounds possessed both oxirane ring and maleimidereactive groups. Each of the reactive groups might formcross-linking networks under thermal curing reaction withcuring agents to bring about high cross-linking density. So itwas considered worthwhile to study the synthesis,characterization and curing reaction of the maleimide epoxycompounds with different amines and to study the propertiesof the cured resin systems (For water resistance and chemicalresistance properties).Experimental SectionMaterials and measurements. Maleic anhydride and 4-aminophenol were purchased from S.d.Fine chemicals. Thefollowing bisphenol-A based epoxy resins were used.(Lapox* make supplied by ATUL Ltd, polymer division); (i)Lapox B-11 (medium viscous liquid; Viscosity at 25 oC,9000-12000 m pas), and (ii) Lapox B-13 (High viscousliquid; Viscosity at 25 oC, 12000-16000 m pas). AEP (1-(2-aminoethyl) piperazine) and IPDA (isophorone diamine)were supplied by Aldrich Chemicals. Triphenylphosphine(TPP), dimethyl formamide (DMF) and toluene were obtainedfrom Merck chemicals. Infrared spectra were recorded usingNicolet FT-IR spectrometer using KBr. Elemental analyseswere carried out in Liquid Crystal Department, RamanResearch Institute, Bangalore. The 1H NMR spectra of MIEcompound is recorded in Sophisticated Instrument Facility,Indian Institute of Science, Bangalore. TGA/DTA for curedsamples is recorded in National Chemical Laboratory, Pune. Synthesis of N-(hydroxyphenyl) maleamic acid (HPMAc).In a 2-necked flask equipped with a mechanical stirrer and areflux condenser, maleic anhydride (0.88 mol, 86.4 g)dissolved in 700 mL acetone was charged. The solution wasstirred at ambient temperature, and 4-aminophenol (0.80mol, 87.2 g) was added in portions over 30 min. The reactionMaleimide Bisphenol–A Based Epoxy Resins  Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10     1543mixture turned into yellow slurry. After stirring for 1.5 h theslurry was filtered. The solid was washed with acetone, andthen dried at 60 oC under vacuum to give light green powderproduct. Yield 95%. Molecular Formula: C10H9NO4. Elementalanalysis: Found % (Calcd %) C: 57.90 (57.97), H: 4.38(4.35), N: 6.80 (6.76). IR (KBr, cm−1): 3312 (N-H), 3200 (O-H), 1703 (-COOH), 1621 (C=O) and 1600 (C=C).Synthesis of N-(4-hydroxy phenyl) maleimide (HPM).In a 3-necked flask equipped with a mechanical stirrer, watersegregation, and a reflux condenser, HPMAc (0.6 mol, 123.2g), p-toluenesulphonic acid (0.05 mol 8.75 g), dimethyl-formamide (60 mL) and toluene (700 mL) were charged.The mixture was heated to reflux for about 8-10 h until theslurry turned into a clear solution and the stoichiometricamount of water was segregated. After removing toluene,the residue was poured into a large amount of water. Theprecipitate was collected with filtration, washed with 5%sodium bicarbonate solution, and with water. The crude productwas recrystallized from a mixed solvent of water-isopropanol(1 : 1) to give brown crystalline needle product. Yield: 64%.Molecular formula C10H7NO3. Elemental analysis: Found %(Calcd %) C: 63.50 (63.49), H: 3.66 (3.70), N: 7.45 (7.41).IR (KBr, cm−1): 3416 (O-H), 1709 (-C=O), 1641 (C=C), and1388 (C-N).Synthesis of maleimide epoxy compounds (MIE). MIEwas prepared by reacting B-13/B-11 epoxy resins and N-(4-hydroxy phenyl) maleimide (HPM). HPM (0.027 mol, 3.74g) and B-13/B-11(12.53 g) were dissolved in 20 mL ofmethylethylketone in a 150 mL round bottomed flask. TPP(0.05 g) was added to the solution as a reaction promoter.The reaction solution was then heated to reflux (at about130-140 oC) for 4h and then cooled at room temperature.The solvent was removed out with rotary evaporator. Theproduct was then heated at 70 oC under vacuum for 6 h togive a semisolid product.14 Yield 90%. Elemental analysis:Found % (Calcd %) C: 69.21 (69.87), H: 5.80 (5.72), N:2.88 (2.96). IR (KBr, cm−1): 3471 (O-H), 1636 (C=O), 1638(C=C), 1367 (C-N), and 917 (oxirane ring). 1H NMR (ppm,in DMSO-d6): 1.54 (s, 6H), 2.64-2.66 (t, 1.2H), 2.77-2.81 (t,1.2H), 3.25-3.28 (m, 1.2H), 3.43 (m, 0.8H), 3.71-3.77 (m,1.2H), 3.95 (b, 3.2H), 4.20-4.25 (m, 1.2H), 5.39 (b, 0.8H),6.71-7.29 (m, 12.8H). Softening point: 110-112 oC. Epoxyequivalent weight (MIEB-13) = 451 (calculated value 445).Epoxy equivalent weight (MIEB-11) = 369 (calculated value362). Preparation of cured epoxy resins. The cured epoxyresins were obtained from thermally curing of maleimideepoxy resin (MIE) with amines such as 1-(2-aminoethyl)piperazine (AEP) and 5-amino-1,3,3-trimethylcyclohexanemethylamine isophoronediamine, IPDA (based on hydrogenequivalent weight) were mixed together in methylethylketonesolution and cured in oven. The conditions of curingreactions for B-13MIE/AEP, B-13MIE/IPDA, B-11MIE/AEP,and B-11MIE/IPDA compositions were 80 oC (1 h).Moisture absorption and chemical resistance measure-ments. The above cured maleimide epoxy resins were cutinto small specimens of 25 × 25 mm and edges of specimenswere coated with the same matrix system in order to avoidthe moisture absorption through cut edges by capillaryaction. All the specimens were weighed bone dry inSartorious balance. To start with, the initial weights werenoted at room temperature.15 The samples were thenimmersed in water/alkali/solvent/acid for different intervalsof time at room temperature. and then taken out, wiped, anddried with tissue paper, and weighed.Results and DiscussionPreparation of MIE epoxy compounds. The preparationof the maleimide-epoxy compounds (MIE) were performedthrough by reacting HPM with a diglycidylether ofbisphenol-A (B-13/B-11) via addition reactions between thephenol group and the oxirane group (Scheme 1). Owing tothe high viscosity of the resulting products, a solutionprocess was carried out for the above mentioned reactionswith 500 ppm of triphenylphosphine as a catalyst andScheme 11544     Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10 S. K. N. Gowda and K. N. Mahendramethylethylketone as a solvent. The epoxy equivalent weightvalues of the maleimide-epoxy compounds calculated fromreaction compositions were consistent with the valuesobtained from titration experiments. This result implies thehigh conversions of the reactions between phenol groupsand oxirane rings. The above reaction was monitored byFTIR (Fig. 5). The decrease in the intensity of the absorptionpeak of the oxirane ring at 917 cm−1 clearly indicated thedecrease in concentration of oxirane rings as the reactionproceeds. The chemical structure of the resulting maleimideepoxy compound obtained was confirmed by the presence ofthe following absorption peaks at 1367 cm−1 (C-N), 1711,1778 and 716 (imide group), and 1698 cm−1 (C=C). Theauthenticity of maleimide epoxy compounds was alsoconfirmed by the elemental analysis. The maleimide epoxycompounds obtained were highly viscous liquid, and thismay be due to incorporation of the heterocyclic hard imido-phenyl groups, and increase of molecular weight.In addition to IR and elemental analysis, the 1H NMRanalysis on the MIE compound also indicated the proposedchemical structure as shown in the (scheme 1) (Fig. 6). Theappearance of the absorption peaks at about 3.95 ppm (ringopened oxirane ring, -OCH2CH(OH)-) and 5.39 ppm (-COH) demonstrated the performance of the additionreaction between HPM and B-11/B-13. The peaks at about2.64, 2.77, 3.25, 3.75, and 4.24 ppm showed the typicaloxirane absorptions, and the peak at 1.54 ppm exhibited theabsorption of the isopropyl group. Moreover, the HPM/B-11/B-13 unit ratios were directly calculated from the peakarea ratios of the absorption at 6.71-7.29 ppm (aromaticproton and CH=CH), and the absorption peak at 1.54 ppm(isopropyl group), and the results were coincident with thefeeding ratios of HPM/B-11/B-13 for every MIE compounds.Additionally, the chemical structures of MIE compoundswere confirmed with the experimental results of elementalanalysis. All the above evidences indicate that MIE obtainedis MI-monobifunctional bisphenol-A epoxy compound.Preparation of cured epoxy resins. The probablemechanism of curing of epoxy oxirane ring with amines andself addition of maleimide groups with curing agents is asshown in Scheme 2 and 3 respectively.17,18In this way a cross-linked structure can be built up.Scheme 2Scheme 3Maleimide Bisphenol–A Based Epoxy Resins  Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10     1545Moreover, the maleimide groups might also crosslinkthrough self-addition reaction under heating during thermalcuring. Since the curing compositions were based on thehydrogen equivalent weight of amines, most of the aminegroups were expected to react with oxirane groups at lowtemperature region. Since almost no amino groups were leftto react with maleimide group, only self-addition reactionswould have occurred for maleimide groups in the curingreaction. The resulting products were expected to possesshigh cross-linking densities. Thermal properties of the cured epoxy resin. Thethermal stability of the maleimide epoxy resins wasinvestigated with thermo gravimetric (TGA/DTA) analysis inair atmosphere (Fig. 7-10). The thermograms of the curedFigure 1. Moisture/Acid/Alkali/Solvent resistance of MIEB-13with AEP at room temperature.Figure 2. Moiture/Acid/Alkali/Solvent resistance MIEB-11 withAEP at room temperature.Figure 3. Moiture/Acid/Alkali/Solvent resistance MIEB-13 withIPDA at room temperature.Figure 4. Moiture/Acid/Alkali/Solvent resistance MIEB-11 withIPDA at room temperature.1546     Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10 S. K. N. Gowda and K. N. Mahendramaleimide epoxy resins clearly indicate that the thermalstability of cured resins was improved with the incorporationof maleimide groups.17,18 With the incorporation of themaleimide groups, the IDT of the epoxy resin was increased(Table 1). The enhancement due to incorporation ofmaleimide groups on the thermal stability of epoxy resinswas thus demonstrated. On the other hand, the IPDT alsosystematically increased with incorporation of maleimidegroups. The high IPDT (Table 1) of the maleimide-modifiedepoxy resins indicates high thermal stability for the curedmaleimide epoxy compounds. Moisture absorption and chemical resistance measure-ments. The above cured maleimide epoxy resins were cutinto small specimens of 25 × 25 mm and edges of specimenswere coated with the same matrix system in order to avoidthe moisture absorption through cut edges by capillaryaction. All the specimens were weighed bone dry inSartorious balance. To start with, the initial weights werenoted at room temperature.15 The samples were thenimmersed in water/alkali/solvent/acid for different intervalsof time at room temperature, and then taken out, wiped, anddried with tissue paper, and weighed.The % moisture absorbed was calculated by measuring theweights of the specimen periodically using the followingequation. The plots of moisture absorption vs. square root of timewere constructed (Figure 1-4) to note the saturation limits ofthe absorbed moisture. From the figures It is observed thatinitially the water uptake increased, and showed a flat profileexhibiting Fickean type behaviour.15 The maximum moistureabsorption under a given condition of temperature andhumidity in case of maleimide epoxy resins with our aminesystems showed a decreasing trend. Further more, it wasobserved that in case of AEP/MIEB-13 and IPDA/MIEB-13% Moisture Abs =(Specimen weight at any time – Weight of the dry specimen)  × 100Weight of the dry specimenFigure 5. FT-IR Spectrum of MIE.Figure 6. 1H NMR Spectra of MIE.Figure 7. Tharmogram Analysis of MIEB-13 with AEPMaleimide Bisphenol–A Based Epoxy Resins  Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10     1547systems, AEP cured resin is more resistant towards moistureabsorption than IPDA. This may be because of the presenceof tertiary nitrogen atom in case of AEP19 (acts as catalyst),which accelerates the curing rate very much, compared toIPDA. This was the case too in the case of B-11.Similar behaviour was observed in case of acid/solvent/alkali resistance measurements (Figures 1-4). The maximummoisture/acid/alkali/solvent resistance content under a givencondition of temperature in case for maleimide epoxy resinswith our amine (AEP and IPDA) systems are shown in theTable 2. These data clearly indicate that the cured maleimideepoxy resin with the curing agents (AEP and IPDA) showsmore resistance to water absorption and other chemicalscompared to the traditional epoxy cured resin with the sameamines.ConclusionPhenylmaleimido group was successfully incorporatedinto bisphenol-A type epoxy resins (B-13 and B-11) to resultin compounds possessing both oxirane ring and maleimidereactive groups. The cured resins obtained by thermallycuring of the maleimide epoxy (MIE) compounds with AEPand IPDA exhibited excellent thermal stability and goodchemical (acid/alkali/solvent) and water absorption resis-tance.References  1. Jones, R. R. In Chemistry and Technology of Epoxy Resins;   Ellis,B., Ed.; Chapman & Hall: London, 1993; Vol. 8, p 256.  2. Hay, J. N.; Woodfine, B.; Davies, M. High Perporm. Polym. 1996,8, 35.  3. Ishikawa, S.; Nakatani, M.; Fukuda, H.; Yamamoto, S. Jpn.Patent 1996, 8, 253.  4. Agag, T.; Takeichi, T. Polymer 1999, 40, 6557.  5. Gaw, K.; Kikei, M.; Kakimoto, M.; Imai, Y. Polymer 1997, 38,4413.  6. Kim, W. G.; Nam, T. Y. J. Polym Sci. Part A: Poly Chem. 1996,34, 957.  7. Park, S. J.; Kim, H. C.; Lee, H. I.; Suh, D. H. MacromoleculesFigure 8. Tharmogram Analysis of MIEB-11 with AEP.Figur 9. Tharmogram Analysis of MIEB-13 with IPDA.Figure 10. Tharmogram Analysis of MIEB-11 with IPDA.Table 1. Thermal Analysis of the cured epoxy resin: evalution withTGA/DTA under air atmosphereSl. No System IDP (oC) IPDT (oC)1 MIEB-13 + AEP 336.5 370.92 MIEB-11 + AEP 350.0 350.03 MIEB-13 + IPDA 315.6 350.14 MIEB-11 + IPDA 345.0 345.0Table 2. The maximum moisture/acid/alkali/solvent resistance content under a given condition of temperature (25 oC).Sl. No System% Weight Gain % Weight lossH2O10%NaOHNH3C2H5OH C6H6H2SO4HCl HNO31 MIEB-13 +AEP 1.56 1.31 1.20 1.70 1.45 3.51 3.21 3.002 MIEB-11 +AEP 1.67 1.41 1.30 1.75 1.55 4.1 3.55 3.103 MIEB-13 +IPDA 1.7 1.45 1.35 1.80 1.60 4.50 3.85 3.854 MIEB-11 +IPDA 1.85 1.55 1.40 1.90 1.65 4.68 4.00 3.501548     Bull. Korean Chem. Soc. 2006, Vol. 27, No. 10 S. K. N. Gowda and K. N. Mahendra2001, 43, 693.  8. Kumar, A. A.; Alagar, M.; Rao, RMVGK. Polymer 2002, 43,693.  9. Musto, P.; Martuscelli, E.; Ragosta, G.; Russo, P.; Scarinzi, G. J.Appl. Polm. Sci. 1998, 69, 1029.10. Kumar, A. A.; Alagar, M.; Rao, RMVGK. J. Appl. Polym. Sci.2001, 81, 2330.11. Kumar, A. A.; Alagar, M.; Rao, RMVGK. J. Appl. Polym. Sci.2001, 81, 38.12. Han, J. L.; Chen, Y. C.; Li, K. Y.; Hsieh, K. H. J. Appl. Polym. Sci.1998, 70, 529.13. White, L. A.; Weber, W. J.; Mathias, L. J. Polym. Bull. 2001, 46,463.14. Shibora, T.; Okuse, S.; Aoki, T.; Kato, H. US Patent 2000, 6, 143.15. Vanaja, A. Ph.D Thesis.; Bangalore University: Bangalore, 2003.16. Wu, C.-S.; Liu, Y.-L.;  Hsu, K.-Y. Polymer 2003, 44, 565.17. Ashcroft, W. R.; In Chemistry and Technology of Epoxy Resin;Ellies, B., Ed.; Chapman and Hall: 1993; Vol. 2, p 37.18. Liu, Y. L.; Liu, Y. L.; Jeng, R. J.; Chiu, Y. S. J. Polm. Sci. Part-A;Polm. Chem. 2001, 39, 1716.19. Shivananda, K. N.; Mahendra, K. N. International Congress ofChemistry and Environment 2005, 337.

Preparation and curing studies of maleimide bisphenol-A based epoxy resins

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Preparation and curing studies of maleimide bisphenol-A based epoxy resins

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